Connection structural body with Cu—Cu bonding and roughened surface deposits

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2022-030088, filed on Feb. 28, 2022, the entire contents of which are incorporated herein by reference.

This disclosure relates to a connection structural body, a semiconductor device, and a method for manufacturing a connection structural body.

Japanese Laid-Open Patent Publication No. 2013-93547 describes a semiconductor device that bonds an electrode pad of a semiconductor element and a connection terminal of a wiring substrate with a solder layer.

The pitch between connection terminals of a wiring substrate has become narrower as a result of sophistication of semiconductor elements. However, when the pitch of the connection terminals becomes narrower, short-circuiting is more likely to occur between adjacent solder layers after reflow soldering is performed. Short-circuiting between adjacent solder layers leads to short-circuiting between adjacent connection terminals.

In one embodiment, a connection structural body includes a first connection terminal, a first roughened-surface copper metal film, a second connection terminal, and a second roughened-surface copper metal film. The first connection terminal includes a first opposing surface. The first roughened-surface copper metal film is formed on the first opposing surface. The second connection terminal includes a second opposing surface facing the first opposing surface. The second roughened-surface copper metal film is formed on the second opposing surface and bonded to the first roughened-surface copper metal film. The first roughened-surface copper metal film includes a structure in which first deposits of copper are piled over one another on the first opposing surface. The second roughened-surface copper metal film includes a structure in which second deposits of copper are piled over one another on the second opposing surface. A bonded portion of the first roughened-surface copper metal film and the second roughened-surface copper metal film includes a structure in which the first deposits and the second deposits are piled such that the bonded portion includes pores.

Embodiments will now be described with reference to the drawings. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. Also, to facilitate understanding, hatching lines may not be illustrated or be replaced by shadings in the cross-sectional drawings. In the present specification, “plan view” refers to a view of a subject taken in a perpendicular direction (for example, up-down direction in). Further, “planar shape” refers to a shape of a subject viewed in the perpendicular direction. In the present specification, “up-down direction” and “left-right direction” refer to directions when the drawings are oriented to an appropriate position allowing reference numerals of the elements to be read correctly. Moreover, in the present specification, “parallel”, “orthogonal”, and “perpendicular” include not only strictly parallel, strictly orthogonal, and strictly perpendicular cases but also include generally parallel, generally orthogonal, and generally perpendicular cases within a range allowing the same advantages to be obtained.

A first embodiment will now be described with reference to.

Semiconductor Device

As illustrated in, a semiconductor deviceincludes a wiring substrate, one or more semiconductor elements(one semiconductor elementin this case), and external connection terminals.

Wiring Substrate

The wiring substrateincludes, for example, a substrate body. A wiring layerand a solder resist layerare formed on a lower surface of the substrate bodyin this order. A wiring layer, an insulating layer, a wiring layer, and a first roughened-surface copper metal filmare formed on an upper surface of the substrate bodyin this order.

The substrate bodymay be, for example, a wiring structural body in which insulating resin layers and wiring layers are alternately arranged one upon another. The wiring structural body may include, for example, a substrate core. Alternatively, the wiring structural body does not have to include a substrate core. The material of the insulating resin layer may be, for example, a thermosetting insulating resin. The thermosetting insulating resin may be, for example, an insulating resin such as an epoxy resin, a polyimide resin, or a cyanate resin. Further, the material of the insulating resin layer may be, for example, an insulating resin having a photosensitive resin, such as a phenol-based resin or a polyimide-based resin, as a main component. The insulating resin layer may include, for example, a filler such as silica or alumina.

The material of the wiring layers of the substrate bodyand the wiring layersandmay be, for example, copper (Cu) or a copper alloy. The material of the solder resist layermay be, for example, an insulating resin having a photosensitive resin, such as a phenol-based resin or a polyimide-based resin, as a main component. The solder resist layermay include, for example, a filer such as silica or alumina.

Wiring Layer

The wiring layeris formed on the lower surface of the substrate body. The wiring layeris the lowermost wiring layer of the wiring substrate.

Solder Resist Layer

The solder resist layeris formed on the lower surface of the substrate bodyand covers the wiring layer. The solder resist layeris an outermost insulating layer (here, lowermost insulating layer) of the wiring substrate.

The solder resist layerincludes a plurality of openingsX formed to expose parts of a lower surface of the wiring layeras external connection pads P. The external connection terminalsare respectively connected to the external connection pads Pand used to mount the wiring substrateon a mounting board such as a motherboard or the like.

When necessary, a surface-processed layer is formed on the lower surface of the wiring layer, which is exposed from the bottom of each openingX. Examples of the surface-processed layer include a gold (Au) layer, a nickel (Ni) layer/Au layer (metal layer in which Au layer is formed on Ni layer with Ni layer serving as bottom layer), a Ni layer/palladium (Pd) layer/Au layer (metal layer in which Ni layer, Pd layer, and Au layer are formed in this order with Ni layer serving as bottom layer), or the like. Examples of the surface-processed layer further include a Ni layer/Pd layer (metal layer in which Pd layer is formed on Ni layer with Ni layer serving as bottom layer), a Pd layer/Au layer (metal layer in which Au layer is formed on Pd layer with Pd layer serving as bottom layer), or the like. The Au layer is a metal layer of Au or a Au alloy. The Ni layer is a metal layer of Ni or a Ni alloy. The Pd layer is a metal layer of Pd or a Pd alloy. The Au layer, Ni layer, and Pd layer may each be, for example, a metal layer (electroless plating layer) formed by an electroless plating process or a metal layer (electrolytic plating layer) formed by an electrolytic plating process. Further, the surface-processed layer may be an organic solderability preservative (OPS) film formed by performing an antioxidation process such as an OSP process on the lower surface of the wiring layer, which is exposed from the openingsX. The OSP film may be an organic coating of an azole compound, an imidazole compound, or the like. When the surface-processed layer is formed on the lower surface of the wiring layer, the surface-processed layer functions as the external connection pads P.

In the example illustrated in, the external connection terminalsare arranged on the lower surface of the wiring layer. Alternatively, the wiring layerexposed from the openingsX or the surface-processed layer formed on the lower surface of the wiring layermay be used as the external connection terminals.

Wiring Layer

The wiring layeris formed on the upper surface of the substrate body. The wiring layeris electrically connected to the wiring layervia, for example, one or more wiring layers and one or more through-electrodes in the substrate body.

Insulating Layer

The insulating layeris formed on the upper surface of the substrate bodyand covers parts of the wiring layer. The insulating layeris an outermost insulating layer (here, uppermost insulating layer) of the wiring substrate. The insulating layermay be, for example, the same insulating layer as the insulating layer of the substrate body. Alternatively, the insulating layermay be, for example, a solder resist layer. The material of the solder resist layer serving as the insulating layermay be, for example, the same material as the solder resist layer.

The insulating layerincludes open portionsX extending through the insulating layerin a thickness-wise direction (up-down direction in) to expose parts of an upper surface of the wiring layer. The open portionX may have any planar shape and any size. In the example illustrated in, each open portionX has a circular planar shape. For example, the open portionX is tapered so that an opening width (opening diameter) decreases from the upper side in(upper surface of insulating layer) toward the lower side (wiring layer).

Wiring Layer

The wiring layeris formed on the wiring layer, which is exposed from the open portionsX. The wiring layerincludes, for example, via wiringV and first connection terminals. The via wiringV is formed in the open portionsX. The first connection terminalsare formed on the upper surface of the insulating layerand electrically connected to the wiring layerby the via wiringV. The first connection terminalsfunction as, for example, electronic component mounting pads that are electrically connected to an electronic component, such as the semiconductor element.

The via wiringV, for example, fills the open portionX and is shaped in correspondence with the open portionsX. The via wiringV has the form of, for example, a reversed truncated cone in which the diameter of the upper surface is greater than the diameter of the lower surface.

Each first connection terminalhas the form of, for example, a rod projecting upward from the upper surface of the insulating layer. The first connection terminalis, for example, a metal post. In the example illustrated in, the first connection terminalis cylindrical. For example, the first connection terminalis formed integrally with the via wiringV. The first connection terminalmay have any planar shape and any size. The first connection terminalmay have a circular planar shape in which the diameter is in, for example, a range from 15 μm or greater to 40 μm or less. The first connection terminalmay have a thickness, for example, in a range from 2 μm or greater to 50 μm or less.

The first connection terminalincludes a first opposing surface(here, upper surface) facing the semiconductor element. The first opposing surfaceof the first connection terminalis, for example, a flat surface. The first opposing surfaceextends parallel to, for example, the upper surface of the substrate body. The first opposing surfaceis, for example, a rather even smooth surface.

In the present specification, “opposing” refers to a case in which two surfaces or two members face each other. Here, “opposing” refers not only to a case in which two parts are entirely facing each other but also to a case in which two parts are partially facing each other. Further, “opposing” includes both a case in which another member is located between the two parts and a case in which no member is located between the two parts.

The material of the via wiringV and the first connection terminalmay be, for example, copper or a copper alloy. In the example illustrated in, the first connection terminalis formed from copper. The via wiringV and the first connection terminalmay each be, for example, an electroless plating layer formed in an electroless plating process or an electrolytic plating layer formed in an electrolytic plating process.

First Roughened-Surface Copper Metal Film

The first roughened-surface copper metal filmis formed on the first opposing surfaceof each first connection terminal. The first roughened-surface copper metal film, for example, entirely covers the first opposing surface. The first roughened-surface copper metal filmexposes, for example, the side surface of the first connection terminal. In other words, in the example illustrated in, the first roughened-surface copper metal filmcovers only the first opposing surfaceamong all of the surfaces of the first connection terminal. The first roughened-surface copper metal filmmay have a thickness (film thickness), for example, in a range from 1 μm or greater to 5 μm or less.

As illustrated in, the first roughened-surface copper metal filmis a plating film having a roughened surface (both upper and side surfaces or only upper surface). The surface (roughened surface) of the first roughened-surface copper metal filmincludes microscopic irregularities. The first roughened-surface copper metal filmincludes a structure in which first depositsof copper are piled over one another on the first opposing surfaceof the first connection terminal. The first depositsmay be flat bodies formed from copper. The first roughened-surface copper metal filmis a plating film formed in an electrolytic copper plating process. The first roughened-surface copper metal filmis, for example, a metal film formed by a plating film including only copper. Here, “structure in which the first depositsof copper are piled over one another” refers to a structure (porous structure) in which a large number of first deposits(electrodeposits), which are formed from a plating metal of copper, are piled over one another in random directions such that a large number of pores are formed in the metal film (plating film).illustrates a partial cross-sectional structure of the semiconductor devicein a state before the semiconductor elementis bonded to the wiring substrate.

The first roughened-surface copper metal filmof the first embodiment includes a structure in which the sheeted (thin plate-shaped) first depositsof copper are piled over one another in various directions such that pores are formed between the sheeted first deposits. Each of the sheeted first depositsmay have a thickness, for example, in a range from 20 nm or greater to 100 nm or less. Preferably, each of the sheeted first depositshas a thickness, for example, in a range from 20 nm or greater to 50 nm or less. The first roughened-surface copper metal filmhas a structure including a stack of layers of a large number of sheeted first deposits. Further, the first roughened-surface copper metal filmhas a three-dimensional nanostructure formed by a large number of first deposits, which are nanoscale microscopic sheets, intersecting one another in random directions and piled over one another in a multi-layer-like manner. Such a first roughened-surface copper metal filmis formed to have a structure in which the sheeted first depositsare densely piled over one another such that a large number of pores are formed between the first deposits. The structure extends over the entire first roughened-surface copper metal filmin the thickness-wise direction of the first roughened-surface copper metal film. That is, the first roughened-surface copper metal filmincludes a large number of microscopic pores throughout the first roughened-surface copper metal filmin the thickness-wise direction. The density of the first depositsvaries, for example, in the thickness-wise direction of the first roughened-surface copper metal film. In other words, the porosity of the first roughened-surface copper metal filmvaries in the thickness-wise direction. For example, the density of the first depositsincreases toward the first opposing surfacein the thickness-wise direction of the first roughened-surface copper metal film. In other words, the porosity of the first roughened-surface copper metal filmdecreases toward the first opposing surface. The overall porosity of the first roughened-surface copper metal filmmay be, for example, in a range from 8% or greater to 20% or less.

In this manner, the first roughened-surface copper metal filmincludes a structure in which a large number of first depositsare piled over one another. Thus, the first roughened-surface copper metal filmhas a roughened surface structure in which the surface is uneven and a large number of pores are included in the thickness-wise direction. The roughened surface structure of the first roughened-surface copper metal filmdiffers from a roughened surface structure formed through a typical roughening process, such as a roughening treatment using a chemical solution or a physical processing. Examples of the typical roughening process include blackening, etching, blasting, or the like.

A roughened surface structureof a comparative example will now be described with reference to. As illustrated in, the roughened surface structureis formed by performing a typical roughening process on the first connection terminalto obtain a structure in which irregularities are formed only in the upper surface of the first connection terminal. The roughened surface structurehas a high density of copper deposits over the entire roughened surface structurein the thickness-wise direction and the widthwise direction (direction orthogonal to thickness-wise direction). The roughened surface structuredoes not include the structure in which the first depositsare piled over one another such as that illustrated in, and pores are not included in the roughened surface structurein the thickness-wise direction or inside the metal film. The porosity of the roughened surface structuredoes not vary in the thickness-wise direction.

As illustrated in, the first roughened-surface copper metal filmis bonded to the first opposing surfaceof the first connection terminal. No intermetallic compound is formed on the interface (bonding interface) between the first connection terminaland the first roughened-surface copper metal film. Thus, the first connection terminalof copper is directly bonded to the first roughened-surface copper metal filmof copper without another member formed from a material other than copper. The first roughened-surface copper metal filmis integrated with the first connection terminal. In the drawings, the first roughened-surface copper metal filmis distinguished from the first connection terminalby a solid line to facilitate understanding. Actually, there may be no interface between the first connection terminaland the first roughened-surface copper metal filmand the boundary may be unclear.

Semiconductor Element

As illustrated in, the semiconductor elementincludes a plurality of second connection terminalsand a second roughened-surface copper metal film. The second connection terminalsare formed on a circuit formation surface (here, lower surface) of the semiconductor element. The semiconductor elementis flip-chip mounted on the wiring substrate. The second connection terminalsof the semiconductor elementare electrically connected to the corresponding first connection terminalsof the wiring substrate. The second connection terminalsare electrically connected to the first connection terminalvia the second roughened-surface copper metal filmand the first roughened-surface copper metal film. This electrically connects the semiconductor elementto the first connection terminalsvia the second connection terminals, the second roughened-surface copper metal film, and the first roughened-surface copper metal film.

The semiconductor elementmay be, for example, a logic chip such as a central processing unit (CPU) chip or a graphics processing unit (GPU) chip. Further, the semiconductor elementmay be, for example, a memory chip such as a dynamic random-access memory (DRAM) chip, a static random-access memory (SRAM) chip, or a flash memory. Multiple semiconductor elementsincluding a combination of logic chips and memory chips may be mounted on the wiring substrate.

Second Connection Terminal

The second connection terminalsare arranged to face the first connection terminals, respectively. Each second connection terminalhas the form of, for example, a rod projecting downward from the circuit formation surface of the semiconductor element. The second connection terminalis, for example, a metal post. In the example illustrated in, the second connection terminalis cylindrical. The second connection terminalmay have any planar shape and any size. The second connection terminalmay have a circular planar shape in which the diameter is, for example, in a range from 15 μm or greater to 40 μm or less. The second connection terminalmay have a thickness, for example, in a range from 2 μm or greater to 50 μm or less.

The material of the second connection terminalmay be, for example, copper or a copper alloy. In the example illustrated in, the second connection terminalis formed from copper. The second connection terminalmay be an electroless plating layer or an electrolytic plating layer.

The second connection terminalincludes a second opposing surface(here, lower surface) facing the first opposing surfaceof the first connection terminal. The second opposing surfaceof the second connection terminalis, for example, a flat surface. The second opposing surfaceextends parallel to, for example, the circuit formation surface of the semiconductor element. The second opposing surfaceis, for example, a rather even smooth surface.

Second Roughened-Surface Copper Metal Film

The second roughened-surface copper metal filmis formed on the second opposing surfaceof each second connection terminal. The second roughened-surface copper metal film, for example, entirely covers the second opposing surface. The second roughened-surface copper metal filmexposes, for example, the side surface of the second connection terminal. In other words, in the example illustrated in, the second roughened-surface copper metal filmcovers only the second opposing surfaceamong all of the surfaces of the second connection terminal. The second roughened-surface copper metal filmmay have a thickness (film thickness), for example, in a range from 2 μm or greater to 5 μm or less.

As illustrated in, the second roughened-surface copper metal filmincludes the same structure as the first roughened-surface copper metal film. The second roughened-surface copper metal filmis a plating film in which a surface (both lower and side surfaces or only lower surface) is roughened. The surface (roughened surface) of the second roughened-surface copper metal filmhas microscopic irregularities. The second roughened-surface copper metal filmincludes a structure in which second depositsof copper are piled over one another on the second opposing surfaceof the second connection terminal. The second depositsmay be flat bodies formed from copper. The second roughened-surface copper metal filmis a plating film formed in an electrolytic copper plating process. The second roughened-surface copper metal filmis, for example, a metal film formed by a plating film including only copper. Here, “structure in which the second depositsof copper are piled over one another” refers to a structure (porous structure) in which a large number of second deposits(electrodeposits), which are formed from a plating metal of copper, are piled over one another in random directions such that a large number of pores are formed in the plating film.

The second roughened-surface copper metal filmof the first embodiment includes a structure in which the sheeted (thin plate-shaped) second depositsof copper are piled over one another in various directions such that pores are formed between the sheeted second deposits. Each of the sheeted second depositsmay have a thickness, for example, in a range from 20 nm or greater to 100 nm or less. Preferably, each of the sheeted second depositshas a thickness, for example, in a range from 20 nm or greater to 50 nm or less. The second roughened-surface copper metal filmhas a structure including a stack of layers of a large number of sheeted second deposits. The second roughened-surface copper metal filmis formed to have a structure in which the sheeted second depositsare densely piled over one another such that a large number of pores are formed between the second deposits. The structure extends over the entire second roughened-surface copper metal filmin the thickness-wise direction of the second roughened-surface copper metal film. The second roughened-surface copper metal filmhas a three-dimensional nanostructure formed by a large number of second deposits, which are nanoscale microscopic sheets, intersecting one another in random directions and piled over one another in a multi-layer-like manner. Such a second roughened-surface copper metal filmincludes a large number of microscopic pores throughout the second roughened-surface copper metal filmin the thickness-wise direction. The density of the second depositsvaries, for example, in the thickness-wise direction of the second roughened-surface copper metal film. In other words, the porosity of the second roughened-surface copper metal filmvaries in the thickness-wise direction. For example, the density of the second depositsincreases toward the second opposing surfacein the thickness-wise direction of the second roughened-surface copper metal film. In other words, the porosity of the second roughened-surface copper metal filmdecreases toward the second opposing surface. The overall porosity of the second roughened-surface copper metal filmmay be, for example, in a range from 8% or greater to 20% or less.